Since a numerical control for instructing the position of a tool to a workpiece by numeric information has advantages of improvement in its productivity, energy-saving, and ease of supervision, numerical control is applied to various machine tools and is widely utilized.
FIG. 1 shows an example of a prior art numerical control. In FIG. a control unit 50 has a central processing unit (hereinafter referred to as "CPU") 52, and a data input/output unit 54 and a signal input/output unit 56 are connected to the control unit 50.
An arithmetic unit 58, a memory 60 and a driving unit 62 are connected to the control unit 50, and a servo motor group 64 is connected to the driving unit 62.
The data input/output unit 54 is for inputting working data from an external data input/output unit, not shown, and for outputting the data to the control unit 50, and the signal input/output unit 56 is for inputting control data such as start, stop, and for outputting the data to the control unit 50.
The memory 60 has a data area 60A and a program area 60B. The working data input from the data input/output unit 54 is stored in the data area 60A, and the control data input from the signal input/output unit 56 is stored in the program area 60B.
The arithmetic unit 58 then performs necessary calculation to control a servo motor group 64, and calculates, for example, to interpolate to obtain a moving distance for a predetermined time by resolving the speed in each axial direction of orthographic coordinates when a driving command is given in terms of a vector speed.
The driving unit 62 has three driving circuits 62A, 62B and 62C corresponding to three servo motors 64A, 64B and 64C of the servo motor group 64.
The servo motor group 64 actually corresponds to the servo motors of each of three shaft driving sections of a machine tool such as a lathe or a milling machine.
Data necessary to control the operation of a machine tool are inputted through the data input/output unit 54 and the signal input/output unit 56 from an external computer. These data are respectively stored by the control unit 50 in the data area 60A and the program area 60B of the memory 60.
The control unit 50 calculates the above-mentioned interpolation by the arithmetic unit 58 from the data stored in the data memory area 60A according to the program and the data stored in the program memory area 60B, and provides instructions necessary to drive the driving unit 62. Thus, the servo motor group 64 is driven to execute a predetermined machining operation according to the input data.
As described above, the servo motors 64A, 64B and 64C of the servo motor group 64 are not independently driven, but are only driven integrally.
The above-described conventional numerical control only operates by the control program stored in the program area 60B of the memory 60, and the servo motors 64A, 64B and 64C connected to the driving unit 62, and cannot independently drive the servo motors 64A, 64B and 64C connected to the driving unit 62.
For example, the numerical control cannot operated both to rotate the tool of a milling machine by the servo motor 64A and to use a lathe by the servo motors 64B and 64C.
Thus, it is necessary to install separate numerical controls as shown in FIG. I for the respective machines. Therefore, when controlling the numeric values of a number of machines, a large installation is required that results in an undesirable increase in the cost.
This invention has been made to eliminate the above disadvantages, and an object thereof to provide a numerical control machine capable of efficiently numerically controlling a plurality of machines at less cost.